1. Field of the Invention
The present invention relates to flow in pipes and control valves, and more particularly, to attenuation of vibration, cavitation and noise in a flow control valve using an internal diffuser.
2. Description of the Related Art
Flow control valves are used to regulate fluid flow by introducing a pressure drop in a fluid stream, regulating flow by varying the pressure drop. Under certain conditions localized high-pressure drops occur, causing vibration and noise problems in a gas service or cavitation in a liquid service. Efforts have been made to avoid localized high-pressure drops by spreading an overall pressure drop among different components of the valve.
For cavitation or noise attenuation, it is desirable to spread the pressure drop taken by a valve over as many components within the valve as possible. Each component has a pressure drop ratio, a ratio of pressure drop divided by inlet pressure to that component. Under specified conditions, a valve must restrict flow which results in an overall pressure drop. This overall pressure drop is divided among the various components within the valve that contribute to flow restriction and thus to the overall pressure drop. The more components there are in a valve for taking pressure drops, the lower the pressure drop ratio for each component.
In U.S. Pat. No. 5,437,305, an inlet diffuser is placed in an inlet to a valve body. The inlet diffuser has a plurality of holes or a plurality of teeth or tines extending into an inlet bore. A portion of the pressure drop through the valve is taken across the inlet diffuser. Diametrically opposite the inlet diffuser, a valve passage inlet diffuser is placed which extends inwardly into a bore in a valve element. As the valve is throttled, the valve passage inlet diffuser meshes with the inlet diffuser to restrict flow through the valve. The pressure drop through the valve is further spread throughout the valve by including a valve passage outlet diffuser. Although improvements such as these have been made in valves to attenuate vibration, cavitation and noise, there remains a need for further improvements.